近百年來，熱帶及亞熱帶地區的人們一直受到由病媒蚊轉播的登革熱所侵擾。受到登革病毒感染的人們可分為有症狀及無症狀者；有症狀的病人會出現典型的發燒症狀，但有少許的病人會發展成重症，如登革出血熱及休克。過去及最近的文獻報告中得知登革熱病人在發燒期常伴隨著低血小板症，同時也觀察到骨髓幹細胞及巨核細胞等細胞數銳減的現象，因此說明了這些細胞與登革病毒感染有密不可分的關係。雖然骨髓幹細非常容易被登革病毒感染，對於可供病毒感染且複製的細胞的表型，目前還無法正確地釐清。由於蚊子在吸血過程中，很可能將病毒釋放到血管裏。因此，我們的假說是在流竄於體內周邊血少量的骨髓幹細胞及巨核細胞很可能成為登革病毒感染的目標。我們收集登革疫區及非登革疫區健康人的周邊血，了解其細胞族群的分佈狀況及進行登革病毒感染。辨識細胞族群於周邊血細胞的表面蛋白標記是利用流式細胞儀來分析然後分類。主要使用的標定蛋白有幹細胞特有的標的CD34，CD133及CD117，巨核系細胞特有的標的CD61及CD41a，以及吞噬性細胞特有的標的CD14，並透過細胞上標的蛋白的排列組合來分辨細胞族群。在周邊血細胞感染的實驗中，我們發現使用MOI=1登革病毒量的感染下，有高達55%的非登革疫區健康人周邊血球細胞可被登革病毒所感染。此外，這些可被登革病毒感染的周邊血球中，巨核系細胞的數量顯著地高於不可被感染的周邊血細胞組，並且與其生產的病毒量具有正向的相關性。讓我們訝異的是，這個現象並沒有在登革疫區健康者的周邊血球細胞中顯現，但登革病毒感染登革疫區健康者的周邊血球細胞的概率則高達73%。藉此我們透過蛋白質譜分析儀分析兩者之間的骨髓幹/前驅細胞的差異，發現登革疫區健康者細胞內特有蛋白的功能與免疫反應及細胞分裂分化的比例上升至少10%。這說明了登革疫區健康者在病毒感染後，骨髓幹/前驅細胞的功能會受到影響和有所改變。更有趣的是，我們發現吞噬性細胞在非登革疫區和登革疫區健康者的細胞比例沒有明顯的不同，但在非登革疫區健康者身上發現可被感染的周邊血球細胞中吞噬性細胞的量與所複製出來的登革病毒量成反比的相關性，因而推測吞噬性細胞所扮演的是清除病毒的角色。進一步的實驗將同個人周邊血純化出的幹細胞、巨核系細胞和吞噬性細胞進行登革病毒感染，結果顯示幹細胞和巨核系細胞產出相當高的病毒量，然而吞噬性細胞僅產生少量的病毒。因此我們認為骨髓幹/前驅細胞和巨核系細胞是周邊血球細胞中被登革病毒所感染的主要目標細胞且是造成嚴重病症的主要相關族群。

Dengue is currently the most important mosquito-borne human viral disease and has been cohabitated with human beings for many centuries. Dynamic clinical manifestations, rang-ing from asymptomatic infection, mild fever, to severe hemorrhagic fever that occasionally accompanies with a high fatality shock syndrome, have been the salient characteristics of the disease. Previous investigations reveal that one of likely cause of thrombocytopenia seen in dengue patients is a likely consequence of dengue virus infecting platelet progenitor cells, megakaryocytes and bone marrow cells associated with this lineage. With its easy ac-cess, peripheral blood mononuclear cells (PBMC) become the major resource for investiga-tion of cells permissive for dengue virus (DENV) infection. Despite many decades of in-tensive efforts, the actual phenotypes of cells accounting for the source of the virus in cir-culation of affected subjects remain unclear. Profiling of cells in PBMC by FACS with markers, such as CD34, CD133, and CD117 for stem/progenitor cells, CD61 and CD41a for megakaryocytic lineage cells, and CD14 for phagocytic cells were performed. The PBMC was then infected with DENV at MOI=1 and infectious virus in supernatants were evaluated by standard plaque assay. Results showed that 55% (12/22) PBMCs from naïve non-endemic individuals were infectable by DENV, but varying in viral titers, and that the percentage of megakaryocytic lineage cells in the infectable PBMC was significantly higher than those non-infectable PBMC. In contrast, there were higher infectable rate, but no sig-nificant different between stem/progenitor cells and viral titer in PBMCs from dengue en-demic individuals. Protein profiling showed that proteins associated with immune respons-es in stem/progenitor cells were higher from dengue endemic individuals, suggested that immune biological processes in these cells were continuing on being sensitized even after recovery from DENV infection. Besides that, the levels of phagocytic cells was slightly higher in non-infectable PBMC group of naïve non-endemic individuals, presuming that phagocytic cells play a significant role in virus clearance rather than a target to be infected. Enriched stem/progenitor and megakaryocytic lineage cells were highly permissive to DENV, with 32- and 100-fold increase of viral titers respectively, compared with that of non-enriched PBMC and phagocytic cells from dengue endemic subjects. In conclusion, the levels of stem/progenitor and megakaryocytic lineage cells in PBMC may prerequisite for the DENV infection and contribute to the disease outcomes upon acquiring the DENV.

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